1. Field of the Invention
The present invention relates to fiber optical systems. More specifically, the present invention relates to methods and apparatus for distributing light in fiber optic systems.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Optical technology has been widely used in digital and radio frequency communication systems. A fiber optic distribution network can significantly increase channel capacity and reduce the weight and size requirements thereof. Fiber optic distribution networks typically include an optical power divider or combiner as a key component.
Optical power dividers/combiners couple light waves between distribution fibers and bundles of fibers. Light wave coupling systems commonly utilized in the past include series and parallel designs for transmitting optical information on an optical carrier. An example of a series light wave coupler is the series-fed, side-wall coupling device. This light wave power distribution device includes a series optical waveguide having a plurality of light tap points along the length of the waveguide. In practice, the optical energy is sequentially tapped off along the optical waveguide.
Because of the series design, the optical energy at the terminal end of the waveguide is dependent upon the optical energy at the entrance of the waveguide and the number of tap points therebetween. Further, the optical signal withdrawn from any particular one of the tap points is out of phase with that withdrawn from each of the other tap points. A phase delay between the tap points exists because there is typically a discrete time delay associated with the tapping of optical energy at each individual tap point due to the series design. As a result, the series-fed, side-wall coupling device produces optical output signals having uneven amplitude and phase due to attenuation and interaction along the tap points of the optical waveguide.
An example of a parallel light wave coupler includes a binary phase grating for star couplers. The grating may be formed from an orderly periodic pattern of scribes on one or both sides of a planar optical transmission medium. In either case, the gratings cause a scattering or diffusing of the light passed through or reflected from the transmission medium at periodic points. The light scattering creates diffusion patterns producing alternating bright and dark spots. An optical receiver, such as a fiber bundle, is typically positioned to intercept the bright spots.
Two binary phase gratings may be crossed at right angles to scatter a light beam into a two-dimensional diffraction pattern of grating lobes. The diffraction pattern of grating lobes are focused by a lens to form a dot pattern. The dot pattern is collectively determined by the periodic structure of the phase grating, the geometry of which must be carefully designed to achieve the desired grid pattern. Unfortunately, the rigid and complex design constrains the spacing and lattice structure of the fiber array. Further, the phase grating approach can not control the power distribution over the fiber array independently. Although this approach exhibits a corporate parallel structure, the phase grating approach relies on the scattering of and the recollection of light. Because of the collective effect of the gratings, there is no control over the resultant optical dot pattern. Thus, for any particular grating design, the resultant dot configuration is limited to, for example, a rectangular pattern. The resultant dot configuration can be modified by changing the orderly periodic pattern of nicks and scribes on the grating. Unfortunately, the resultant dot configuration is again limited by the modified periodic pattern on the grating.
Thus, there is a need in the art for an improvement in light wave coupling devices in conventional fiber optic systems.